GM Service Manual Online
For 1990-2009 cars only

Z Height

Trim height is a predetermined measurement relating to vehicle ride height. Incorrect trim heights may cause symptoms similar to alignment problems. Check the trim heights when you diagnose steering or vibration complaints.

The Z dimension measurement determines the proper ride height for the front end. The Z dimension is different for RWD vehicles and 4WD vehicles. The 4WD vehicles have different points of measurement to determine Z height. Use the torsion bar adjusting arm in order to adjust Z height. RWD vehicles have no adjustment and could require replacement of suspension components.


Object Number: 88  Size: SH

On RWD vehicles, measure Z height from the center line of the bolt of the front lower control arm down to the lower inboard corner of the ball joint. Trim all Z heights at 67.0-79.0 mm (2.6-3.0 in).


Object Number: 91  Size: SH

On 4WD vehicles, measure Z height from the center line of the pivot bolt (1) down to the lowest inboard edge of the steering knuckle (2).


Object Number: 92  Size: SH

Trim all curb Z heights at 114.0-128.0 mm (4.6-5.0 in). In order to adjust Z height, turn the bolt that contacts the torsion arm as needed. One revolution of the bolt into the nut increases the Z height by 6.0 mm (0.2 in) (1).

Z Height Measurement

Measure the Z height using the following procedure:


    Object Number: 96  Size: SH
  1. Lift the front bumper of the vehicle up around 38 mm (1.5 in).
  2. Gently remove your hands. Let the vehicle settle by itself.
  3. Repeat the jounce operation two more times for a total of three times.
  4. Measure the Z dimension.
  5. Push the front bumper of the vehicle down about 38 mm (1.5 in).
  6. Gently remove your hands. Let the vehicle rise by itself.
  7. Repeat the jounce operation two more times for a total of three times.
  8. Important: True trim height is the average of the high and low measurements.

  9. Measure the Z dimension.
  10. Find the average of the high and low measurements. This is the true Z dimension.

D Height

The D dimension measurement determines the proper rear end ride height. There is no adjustment procedure. Repair may require replacement of suspension components.


Object Number: 93  Size: SH

All vehicles require a measurement from the bumper bracket down to the top of the rear axle housing tube. Trim D height at 130.7-161.5 mm (5.1-6.4 in).

D Height Measurement

Measure the D height using the following procedure:


    Object Number: 155454  Size: SH
  1. Lift the rear bumper of the vehicle up around 38 mm (1.5 in).
  2. Gently remove your hands. Let the vehicle settle by itself.
  3. Repeat the jounce operation two more times for a total of three times.
  4. Measure the D dimension.
  5. Push the front bumper of the vehicle down about 38 mm (1.5 in).
  6. Gently remove your hands. Let the vehicle rise by itself.
  7. Repeat the jounce operation two more times for a total of three times.
  8. Important: True trim height is the average of the high and low measurements.

  9. Measure the D dimension.
  10. Find the average of the high and low measurements. This is the true D dimension.